Sedimentation apparatus



March 10, 1936. w. c. WEBER 22,033,213

- SEDIMENTATION APPARATUS Original Filed Dec. 24, 1928 4 Sheets-Sheet 1T f Q Q Y Z'mnentor WILLIAM awe BER attorney March 10, 1936.

w. G. WEBER.

SEDIMENTATION APPARATUS.

Original Filed Dec. 24, 192 s 4 Sheets-Sheet I 2 o o a m k T\ K h Q H mm6n 8 m nm 3 @w @v i 7 km I Snvntor. WILLIAM QVYEBER W Gttorneg March 10,1936. w c. WEBER 2,033,213

SEDIMENTATI ON APPARATUS Original Filed Dec. 24, 1928 4 Sheets-Sheet 5Zhmentor WILLIAM C. WEB ER March 10, 1936. w Q WEBER sED lMENTATIoNAPPARATUS Original Filed Dec. 24, 1923 4 Sheets-Sheet 4 WILLIAM G. WEBERPatented Mar. 10, 1936 I 2,033,213 SEDIMENTATION APPARATUS William G.Weber, Larchmont, N. Y., assignor to The Dorr Company, Inc., New York,N. Y., a corporation of Delaware Original application December 24, 1928,Serial No. 328,155. Divided and this application September 2, 1932,Serial No; 631,522

4 Claims.

This invention relates to improvements in apparatus for removing solidparticles from liquid suspension by sedimentation and mechanical removalof the settledsolids, and particularly to apparatus of this type adaptedto remove only the solids having a settling rate above a predeterminedminimum. The apparatus is adapted for continuous operation and comprisesin general the combination of. a primary settling chamber having a mechanism for discharging settled solids, with a secondary treating stationor zone receiving the settled solids and having mechanism forselectively removing such solids from the liquid. While the apparatusmay be operated in different ways to suit various conditions andmaterials, it is especially adapted to the efllcient removal fromflowing liquids of a portion of the solids suspended therein, thesettling chamber operating as a hydroseparator in which the more 'slowlysettling solids, referred to as the undersize, pass out with theoverflow, while the settled solids which in hydroseparators alwaysinclude a substantial amount of undersize are discharged into theselective classification stationor compartment where the undersize isremoved or rejected by the classification station and returned to thesettling chamber.

This arrangement produces efficient classifica-"h tion of the solidssince hydroseparation produces an overflow free from oversize but withconsidneither element can be materially changed in de-,

sign or operation without substantially affecting the other.Furthermore, such arrangements are not adapted to certain operatingconditions, such for instance as the treatment of large flows of. liquidto remove a proportionately small amount of oversize, which requires alarge settling chamber designed on the basis of the rate of flow, with arelatively small classification compartment designed for efiicienthandling of the small amount of oversize, and operating with thesettling chamber as a single classification apparatus.

which returns to the settling,

An important object of this invention is therefore the combination of asettling chamber and a classification compartment so that it may form aunitary apparatus in which the settling chamber can be designed andoperated in conformity with established principles of sedimentation andhydroseparation, and of any suitable material including concrete, whilethe classification compartment can likewise be designed and operatedaccording to the established technology of classification withoutlimitation by the settling chamber construction and operation.

A further object is to provide an eflicient continuous mechanicallycleaned sewage grit chamber, for which purpose the embodiment of theinvention hereinafter described in detail is intended. According topresent practice sewage is passed through long parallel channels inwhich the granular material or grit settles out. These channels are cutout in turn when a suflicient amount of grit is collected and the gritis removed by grab buckets or the like. non-granular or organic matteris necessarily included with the grit thus removed, it is necessary tosubject the grit to a washing operation to remove such organic matterwhich would otherwise render the grit highly ofiensive. 1

As a substantial amount of Although various forms of wet classificationap- I paratus have been well known for a long time, it has been foundimpractical heretofore to separate the grit from sewage by standard wetclassification methods or apparatus which have been successful in otherfields of use, owing to the relatively small amount of grit in ordinarysewage, the great fluctuations in the sewage level betweendry weatherflow and storm flow, and particularly to the difliculty of separatingfrom the grit certain types of solids, including some of an adhesivenature, together with rags, paper and the like which cannot be removedefllciently by standard classification methods and which tend to rendersuch types of classification mechanis unsightly and offensive after ashort period f use. For convenience all solids in the sewage except gritwill be referred to herein as organic matter.

According to the present invention the grit is initially removed fromthe sewage by sedimentation ina large comparatively shallow chamber or'tank, the settled grit and entrained organic matter being conveyed bymechanical scrapers to the secondary zone of treatment such as a bay orother compartment which preferably is located marginally of the primarychamber and in direct connection therewith. In this compartment is 65the supporting and guiding arrangement of the located a classificationapparatus which not only removes the grit mechanically, but which isadapted to exert a liquid. agitative influence in order to agitate thegrit sufllciently to throw the entrained organic solids into suspensionwhereby they are rejected from discharge by the classifier apparatus andreturned to the main settling chamber, from which they are dischargedwith the overflow, leaving a clean grit for ejection or discharge fromthe secondary compartment.

It has been found advantageous to employ in the secondary compartment areciprocating rake mechanism of the type used in standard wetclassification apparatus, as the reciprocating action is highlyeflective in producing the exact amount of agitation desired, and thedesign and operation of this type of classifying apparatus has beenthoroughly worked out and is widely understood.

Classification apparatus of the desired type requires a sloping bottomor inclined deck in the secondary compartment, the grit being dischargedover the upper end of such bottom substantially above the water level.It has been found that it is impossible with present known apparatus ofthis type to remove organic matter which is still included with the gritas the latter reaches the surface of the liquid, since there is notsufficient depth of liquid to carry oif the organic matter at thispoint. An important object of this invention is to provide anarrangement whereby any undersize or more slowly settling solids such asorganic matter reaching this point may be removed from the grit by anovel overflow or backflow arrangement. The slope of the bottom or deckof the classification compartment is determined within narrow limits bythe characteristics of the grit; and as the deep end of this compartmentis located in the most convenient position to receive the settled solidsfrom the primary chamber, the upper or solids discharge end of thecompartment may be located at some distance from the settling chamber. Afurther object of the invention is the provision of a convenientarrangement whereby the backflow or overflow from such compartment ad-=jacent the liquid level at the grit discharge end may be returned bygravity to the settling chamber regardless of fluctuations in liquidlevel. Another objectis the provision of a lateral overflow arrangementat this point which will minimize the return of grit to the settlingchamber with such overflow.

Other objects and advantages of the invention will be apparent from thefollowing description taken -in connection with the accompanyingdrawings in which:

Fig. 1 is a plan view of one type of apparatus in a duplex arrangement;

Fig. 2 is a vertical section on line 2-2 of Figure 1;

Fig. 3 is a vertical section on line 3-3 of Figure 1;

Fig. 4 is an enlarged fragmentary view showing scraping apparatus forthe primary settling chamber;

Fig. 5 is a section on line 'I5 of Figure 1;

Figs. 6, 'I and 8 are diagrammatic views taken generally in verticalsection longitudinally of the raking apparatus in the secondarycompartment and illustrating the discharge of lighter solids carried upby said mechanism;

Fig. 9 is a perspective view of the passage for the discharge of suchlighter solids at a point beyond the primary settling chamber, and

Fig. 10 is a similarview showing discharge directly into the primarysettling chamber.

The primary settling chamber 20 may be of any desired shape, gritchambers now in general K to employ a mechanism of the rotating type,and.

to have such mechanism arranged to impel the settled solids outwardlyfor discharge in a suitable zone at the periphery or margin of the tank,as this permits very convenient location of the secondary or solidswashing compartment, within the same tank, if desired. In the preferredform illustrated a rectangular chamber is disclosed, since such chambersprovide the greatest economy of space, being particularly desirablewhere concrete construction is employed, and, by permitting even uniformflow directly across the chamber result in a maximum decrease invelocity, uniform velocity at all points in the chamber, and aconsequent efliciency in settling out the solids in a minimum of groundspace.

The form shown is designed for use as a sewage grit chamber and lies inthe path of a flowing stream of sewage. The sewage enters through thesewer 2| and passes through the influent channel 22 into the settlingchamber 20 through inlet openings 23 extending substantially throughoutthe length of one side of the settling chamber 20, and arranged to givea substantially even flow into the chamber at all points. This isconveniently accomplished by suitably tapering channel 22, and byproviding distributing vanes 24 adapted to deflect an appropriate partof the influent sewage from channel 22 into the chamber 20. These vanes24 may comprise vertical blades of concrete suitably streamlined inhorizontal section and mounted in openings 23 by vertical spindles 25accessible for setting the vanes at the desired angles to regulate theproportion of flow'into the tank at any given point.

The liquid flows uniformly across the entire chamber at a greatlyreduced velocity, the size of the chamber being designed to permit apredetermined period of detention for the pool of liquid, this periodbeing suflicient for all solid particles having a settling rate above agiven predetermined rate to settle to the bottom of the chamber or pool.The remaining solids, if any, together with the liquid overflow a weir26 (Fig. 5) into the eilluent channel 21, connecting with the outletsewer 28. A suitable bypass 29. may be provided extending around thechamber 20 between the normally shut off by gates 30. When it is desiredto shutdown the apparatus said gates can be sewer 2| and the outletsewer 28, from which it is opened. and suitable gates placed in theguide a rotary framework 33 (Figs. 3 and pivotally supported on a pillar34 in the center of the chamber 28 at a point above the high waterlevel. The vertical scraping blades or rakes 35 extend downwardly fromthe arms 32 and are inclined or set at such an angle that by rotation ofthe framework and arms the rakes 35 engage settled solids and impel themtoward the periphery of. the chamber 26. At the outer end of each arm 32suitable means such as scoop 36 is provided for collecting settledsolids raked into its zone of travel and carrying same to a suitabledischarge opening or chute. In the form shown the scoop is formed of avertical curved strip of metal' mounted below an arm 32 with its wall'nearest the center substantially parallel to the rakes and its outerwall having a slight inward inclination from its leading edge to thepoint of connection with the central wall, preventing the wedging ofgrit between the outer wall of the scoop and the wall of settlingchamber 28. It will be apparent that the arms 32 will serve to collectall solid matter settling in a circular zone extending from the pillar34 to the path of scoops 36, depositing such material in the path of thescoops.

For collecting solid material settling outside the zone of action ofarms 32 particularly in the corners of chamber 20, and 'for rotating theframework 33 and the rake arms 32, a sliding frame 31 is mounted onframework 33 and track 38 exending around the periphery of chamber 20.The outer end of the sliding frame 31 carries a wheel 39 (Fig. 5)resting on track 38 to support one end of the frame, with suitable drivemeans for rotating the wheel. The drive may include a motor 40 mountedon frame 3'1 and driving through belt 4| the pulley 42 on the shaft ofWorm 43 which rotates worm wheel 44 whose shaft carries bevel gear 45meshing with bevel gear 46 on the shaft of the wheel 39. Guide rollers47 at opposite sides of the track 38 keep wheel 39 in position on thetrack.

The central end of sliding frame 31 is supported on the rotary framework33 so as to impart rotary motion thereto and permit the necessarylongitudinal movement of frame 31 as the wheel 39 approaches and recedesfrom the cor-' ners of the chamber 28. One arrangement is shown inFigure 4, in which the rotary framework 33, supported on pillar 34 bysuitable rollers 41, carries the longitudinal channels 48 of frame 31 onrollers 49, and carries rollers 50 on vertical axes engaging the innerfaces of chan-' nels 48 to prevent lateral displacement and to impartthe necessary rotary movement to the framework-33. A central pivot pin5| projecting from the top of pillar 34 and socketed in framework 33prevents lateral displacement of the framework on the pillar.

A suitable collecting device is mounted on the frame 31 for scraping thecorners of chamber 28, and may comprise a scoop 52 of the same generaltype and construction as scoops 36 having a sufficient spread to coverthe distance between the extreme corner of the chamber 20 and theadjacent path of scoops 35. (Arm 32a extending toward scoop 52 should besuitably shortened to avoid interference, and carries no scoop 36).Scoop 52 may be mounted on frame 31 by hangers 53 and 54 connecting thetop plate 52a extending across the entire top of the scoop, to the sidechannels 48 of the frame 31 adjacent the outer and center ends thereofrespectively. It has been found that hangers 53 and 54 are efficaciousin breaking up any ice which forms in the settling chamber.

The secondary compartment or bay may be located in any position where itcan readily receive the settled solids discharged marginally from thesettling chamber 28 and return to said chamber any excess of liquid,together with any more slowly settling solids which it is desired toretain in the liquid. A convenient arrangement for this purpose,particularly designed for concrete construction, comprises a secondarytrough-like or classifying compartment 55 having a sloping bottom withits deep end adjacent the periphery of chamber 28 in position to receivesettled solids raked and discharged outwardly from the chamberand withits upper end above high water level. Suitable mechanism is provided forraking the settled solids upwardly along the bottom and ejecting ordischarging them in a drained state from the upper end, the mechanismbeing operable either to rake all settled solids to discharge withoutthrowing them into suspension, or to produce adjacent to the mechanism azone of sufficient agitation to throw the lighter solids into suspensionso that they may return to the chamber 28. The latter operation isdesirable when the apparatus is functioning as a sewage grit chamber,the agitation serving to wash or otherwise free organic solids from thegrit to produce a clean, inoffensive grit without further treatment.

While a considerable variety of mechanisms for performing either or bothof these solids washing or classifying functions either intermittentlyor continuously is known, apparatus of the reciprocating rake type ispreferred since the proper construction and operation of apparatus ofthis type to produce any desired amount of clas-.

sifying action, or a simple conveying action, is well understood bythose skilled in the art. The preferred form illustrated thereforediscloses the use of the well known Dorr Classifier mechanism shown inUnitedStates Patent No. 1,156,543 issued October 12, 1915.

This arrangement, shown best in Figs. 1 and 2, includes a secondary orclassifying compartment 55 communicating with one side or margin ofchamber 28immediately adjacent thereto, having a sloping bottom or deck56. A chute or incline 51 directs sludge from the collecting device inchamber 20 to the classifying compartment 55,

the chute being preferably located adjacent the center of the side ofsaid chamber and extending into the chamber bottom a distance sufiicientto permit scoops 36 and 52 to discharge their contents laterally througha restricted marginal exit' to be acted upon by the solids washer orclassifier. This apparatus, ordinarily referred to as a classifiermechanism, includes a plurality of transverse scraping blades or rakes58 mounted on longitudinal channels 59 having hanger plates 60 connectedby links 6| to the lower arms of bell cranks 62 and 63, the upper armsof which are connected by reach rod 64. The upper bell crank 62 has adepending arm 65 engaging cam 66 on drive shaft 61, 'the cam impartingthrough the bell cranks a suitable periodic movement to the rakes towardand from the bottom 56 of the compartment 55. A crank 68 on shaft 61carries pitman 69 pivotally connected to drive plates 10 on the channels59, imparting reciprocating movement to the rakes 58 in line with thebottom 56 of compartment 55.

The lower bellcrank 63 may be pivotally supported at the end of an armof the lifting bellcrank H carried by a transverse rod journaled on theside walls of the compartment 55, the upper arm of bellcrank ll beingconnected by a cable 12 to a drum 13 which when rotated will liftbellcrank 63 and thelower end of the raking mechanism as a unit.

The spray pipe 14 may be employed, extending across the compartment 55and provided with the usual line of perforations positioned to projectwash water on the sand or grit at approximately the zone of emergencefrom the liquid. To compensate for the substantial changes in waterlevel encountered in sewage operations pipe 14 may be rotatable in itsjournals I5 on the inside walls of the compartment 55, and may beprovided with handles 16 by which the spray may be directed at theproper zone according to the height of the water or sewage. Where aduplex construction is employed as shown in Figure l, the two rakingunits should be offset on the drive shaft 61 by 180 degrees so thatgravitational pull of the mechanism on the return stroke of one unitwill assist in the advance raking stroke of the other unit, producingmore even load on the motor, asset forth in the above mentioned Patent1,156,543.

An important feature of this invention is the arrangement of thesecondary compartment 55 for the backfiow to the primary chamber 20 ofliquid from said compartment, together with any solids that are insuspension in the liquid due to rejection thereof by the solids washingclassifier and the agitative influence thereof. For this purpose it isadvantageous to have open com;- munication between the side of thesecondary compartment 55 and the settling chamber 20 as is shown in theembodiment illustrated, such communication being broken only by anypillar 'I| that may be'necessary to support the wall carrying the track38 or other superstructure.

It has been found in practice that the type of settled-solids beinghandled, together with the amount of draining and agitation required forany particular operation, will determine very accurately the slope ofthe compartment bottom 56; and as already indicated, it is desirable tohave the lower end of said bottom in .a position determined by the mostconvenient point of discharge of the settled solids. Under theseconditions the compartment bottom or inclined deck 56 may rise abovehigh water level while still adjacent the settling chamber 20; underwhich conditions it is necessary only to provide lateral open connectionbetween compartment 55 and chamber 20 extending generally at least fromnear high water level to below low water level (the exact position ofthis opening being determined by factors hereafter set forth in detail).This arrangement is illustrated in the perspective view in Figure 10.

Under other conditions the compartment bottom 56 will have its zonebetween high and low water marks located at some distance from theprimary settling chamber 20, either because of the necessary length ofcompartment 55, because of the contour of the chamber 2|! or because ofthe relative arrangement of chamber and compartment. Under theseconditions an arrangement must be provided for the release of liquid,with any solids suspended therein, from the compartment 55 in a zonewhere the compartment is not in direct communication with chamber 20. Itis of course necessary to include in the arrangement means forpermitting the escape of liquid without any substantial amount of grit.

In the construction illustrated, and shown best in Fig. 9, an outlet isprovided in one side of the compartment 55 adjacent the portion ofbottom 56 between high and low water marks. This outlet should besubstantially parallel to the bottom and immediately adjacent thereto;but

preferably is slightly above the bottom, providing a ledge 18 forretention of the grit. A discharge deck 19 may be employed, forming thebottom of the outlet, over which the liquid flows into a dischargepassage having a sloping bottom BI ,and discharging into the settlingchamber 20 position superelevated above the liquid level of the i mainbody. This superelevating or creation of waves is progressively carriedout as indicated in Figures 6 to 8. wherein it can "be seen that theliquid between adjacent rakes is higher as the upper sloping end of theclassifier is approached. It is in thissuperelevated zone that theagitation or surge therein causes separation and flotation of theorganics-from the grit. This effect, illustrated in Figure 6, isutilized in the discharge arrangement shown in Figure 9, since theliquid thus raised above normal level by the rakes flows laterally overthe deck 19 at a suitable velocity, serving to carry off the lightersolids without permitting them to settle again on the grit. That is theside or lateral outlet from this superelevated zone is communicatedthrough the apertures 88. Such an arrangement produces a lateral orcrosswise fiow of the liquid across the classifier in this zone and thislateral or sideways flow carries with it the floating or substantiallyfloating, organics.

Thus, the organics are promptly removed from the zone of superelevationor of separation from the grit, as soon as their separation takes place.

Where the lateral flow arrangement indicated is employed, it isdiflicult to prevent the dis charge of a substantial amount ofgrit withthe lateral overflow carrying the organic solids back to the settlingchamber; and while ledge 18 will serve to retain the grit, it willlikewise entrap a certain amount of liquid. It has been found,

in practice however that with the reciprocating rake type of classifier,the rise of the rakes at the end of the feed stroke will suddenlyrelease the liquid thus entrapped, and such liquid flowing back over thesurface of the sand will wash the surface clear of any' organicresiduum, which is returned to a zone from which it can readily overflowon the next stroke of the rakes. It has also been found that thelocation and extent of the discharge 83 is very important where areciprocating rake classifier mechanism is used. It will be apparentthat the discharge 83 must be of suflicient extent to accommodate thesubstantial fluctuations in liquid level encountered in sewagetreatment. Consequently the lower end of the discharge 83 must besufficiently below water level to permit overflow when the sewage is atits lowest level. It has been found, however, that where deck 19 is usedit is not necessary to locate the upper end of passage 83 at the highestlevel of liquid raised by height, since the overflow onto deck 19 willfiow back along the deck a substantial distance, this distance beingdetermined by the point at which such backfiow meets the upward surge ofthe liquid due to the next stroke of the rakes. The upper end ofdischarge 83 therefore may be located this distance below the upper endof deck 19, the latter being of course at the highest point where anylateral overflow can occur.

Where there are extreme changes in sewage level there may at times be atendency for the grit to overflow across deck 19, especially near thelower end thereof, when the sewage is at a high level. In order todecrease this tendency means may be employed for restricting the lateraloverflow across deck 19. The level of the bottom of the dischargeopening 83 may be adjustably raised, as 'by weir boards 85 set in slots86, or a plurality of smaller openings may be substituted for the openpassage 83, as by a suitable partition 81 (Fig. 8) which may be set inslots 86, extending above high water level and provided with a series ofdischarge openings 88 parallel to and adjacent the deck 19, the open--ings being designed and arranged to permit discharge of the liquid whilerestricting its velocity,

. particularly toward the lower end of the deck 19.

This restriction will be particularly efiicacious since under high waterconditions the sewage level behind the partition 81 will approach thelevel on the grit discharge side, reducing further the tendency for highvelocity at points substantially below the liquid level.

It will be understood that while deck 19, ledge 18, and the elongatedoverflow arrangement are all highly advantageous and useful underordinary conditions, changes in the type of mechanism employed, thearrangement of the compartment and the material operated may readilyproduce conditions under which these features are not necessary.

From what has preceded and more particularly in connection with theaccompanying drawings it will be noted the invention of the present caseis directed to a sedimentation basin or settling tank having aparticular type of discharge, to wit, a small or restricted marginaldischarge and that the settling tank also has or is provided with asludge conveying and transferring mechanism particularly constructed forimpelling and collecting settled sludge into a defined collecting zoneor path by a step by step movement of inclined blades or rakes 35 andfor transferring the collectedsludge forwardly along said path directlyto-the marginal discharge.

The inclined blades or rakes 35 and the supporting members or arms 32are operated so that thereby there is provided what may be termed asludge collecting mechanism for progressively impelling, by step by stepmovement, sludge settled at the bottom of said sedimentation basin intoand along the transfer path or defined collect- ,ing zone at the bottomof said sedimentation extent the scoops 52) extend across the collectingzone or transfer path and are supported at the ends of the arms ormembers 32 (or in the case of scoops 52 by mechanism at the ends of arms32) and are operated in such a manner as to provide what may becollectively termed a sludge transfer mechanism particularly since these5 scrapers or scoops and the operative means therefor serve to transferforwardly or ahead of the same to the restricted or small marginaldischarge the collected sludge impelled into the path of the transferscrapers or scoops 36 because of the angular disposition or inclinationof the blades or rakes 32. It will be clear that the path of scrapers orscoops 36 actually parallel, and that the path of the scoops 52effectively parallel, the movement of the inclined blades or rakes 35.15 The mechanism which includes the inclined rakes. or blades, and thescrapers or scoops as 36 may be referred to as means for collectingsettled sewage sludge along a defined zone or path and for transferringthe collected sludge along said path to the restricted or smalldischarge;

The collecting zone or transfer path extends to and in effect terminatesin the small or restricted marginal discharge referred to and there is asloping or inclined fiqor portion, as 51, leading to a. receiving spaceprovided in the classifier and which inclined floor facilitates thedirecting of the sludge being transferred from the large main section ofthe bottom of the sedimentation basin into the desired section of theclassifier.

Conclusiveiy, the method herein employed of collecting and removing thesettled solids from the bottom of the tank is based upon the idea ofcollecting settled sewage solids from diverse points of the bottom inmovements which may be said to be of convergent and/or of compoundcharacter towards and to a marginal point or terminal at the bottom, ina manner to make the thus collected solids amenable for withdrawal.Therefore, the apparatus includes a system of 40 raking blades which arein cooperative relationship with the solids-advancing scrapersor scoopsalso calledpush-ers. That is to say, the pushers move along a narrowsection or zone of the bot tom area, which section terminates at alocation or point of solids withdrawal which may herein suitably becalled a' terminal. The inclined blades deliver solids from diversepoints of the bottom onto the narrow section or zone, while the pushersare so arranged and constructed that in moving along the narrow sectionor zone they advance the solids in a positive fashion along the zone andto the terminal from where they can pass from the tank.

With respect to the preferred embodiment or example illustrated, whichprovides an outwardly I raking rotary rake element such as the rake arm32 with its inclined raking blades 35, and which rake arm has thesolids-advancing scoop or pusher 36 attached to its free end portion, itcan be said in a more specific sense that the rotary rake element iseffective to convey the settled solids essentially forwardly andoutwardly with respect to the direction of rake movement and in ageneral direction leading towards the marginal boundary walls of thetank into a, zone which is substantially peripheral to the areatraversed by the rakes. The pusher advances the solids along that zoneto the marginal point of solids withdrawal or outlet in a positivemanner, that is to say in a manner to avoid an outward forcing of thesolids against the walls, and thus to avoid obstructional marginalsolids accumulation between the walls and the raking element.

I claim: 1. Apparatus of the class described comprising 'a sedimentationchamber located in a flowing of sewage, a substantially rectangularsettling chamber through which the stream flows along a relativelylongitudinal straight path, said chamber having a substantiallyhorizontal bottom for solids to settle thereupon having in each sidethereof a substantially vertical boundary wall and also having asubmerged point of discharge for the settled solids, which saidsubmerged point of discharge is non-central in respect to the bottom andis marginally arranged intermediate the ends of the sides of thechamber; and solids conveying rotatable mechanism comprising radiallyextending raking arms carrying inclined plates providing plows, andcollectors having members in effect providing pushing scrapers, saidplows having circular bodily movement for the impelling outwardly into acircular collecting zone that is immediately below the path of movementof the pushing scrapers of solids settling into a circular area that iswithin said circular collecting. zone, said pushing scrapers beingcarried by and rotatingwith said-arms and being effective to positivelyconvey and push th solids ahead of the same and along said circ arcollecting zone to said discharge, said solids conveying rotatablemechanism also having associated therewith and as a part thereofauxiliary scoop means movable relative to certain of said radiallyextending raking arms and which said auxiliary scoop means is providedfor collecting and conveying solids lying beyond said circularcollecting zone whereby such solids as settled beyond said circularcollecting zone will also be passed to said point of discharge.

3. Settling apparatus according to claim 2 in which the outermost marginof the circular collecting zone is substantially tangential to a sideboundary wall and in which the discharge for the settled solids issubstantially at the point of tangential contact of the circularcollecting zone with said boundary of the chamber.

4. Settling apparatus according toclaim 2 in which the conveying meansthat Iunctions to collect and convey settled solids within and from thearea lying beyond said circular collecting zone comprises alongitudinally slidable arm that is guided from the periphery of thesettling chamber and which is slidable co-axially with said impellingmeans and upon which and by which longitudinally slidable arm there iscarried a scooping member of the auxiliary scoop means.

WILLIAM C. WEBER.

